Environment is getting more and more polluted and contaminated day by day with the release of hazardous substances including toxic substances or materials and wastes into the environment. Environmental pollution is causing not only irreparable damage to the flora or fauna and the marine life but also forcing climatic changes. It is becoming a matter of grave concern to the entire world. There are various reasons for the environmental pollution like effluents and wastes being generated due to industrialisation and urbanization and accidental spillage and/or careless release or dumping of oil and other petroleum products, industrial effluents or wastes, sludges, residential wastes or the like into the environment or water bodies. Beaches are getting polluted with spills of petroleum products like crude oils, fuels or solvents or wastes from ships or ship repairing or dismantling activities or recycling activities in ocean, in ports, harbours or docks or from ship-wrecks or from busting or leakage of oil pipelines.
Contamination of soils, sediments and sands with hazardous or toxic chemicals and wastes is becoming an event of frequent occurrence and the magnitude of its adverse impact is ever increasing. Pollution is becoming a major problem in oceans, on coasts and beaches, in wetlands and surface water bodies, underground aquifers and industrial and commercial sites and needs effective solution for the survival and well being of the habitat.
Accidental spills of oily petroleum products into the sea continue to occur in various parts of the world from time to time creating havoc. For example, the Exxon Valdez incident in Prince Williams Sound, Ak., in March, 1989, the oil spill from oil wells in Kuwait that caused fire during Iraq-Kuwait-USA war during late 1989 and the BP (British Petroleum) oil spill that occurred recently. BP oil spill reportedly poured over one million tonnes of crude oil into the Gulf of Mexico in April, 2010. Recently, off the Mumbai coast, oil spilled from the ship “MSC Chitra” after collision with the ship “m v Khalijia-III” on Saturday morning, 7 Aug. 2010. An alarming level of oil got spilled into the ocean (nearly 1,000 tonnes) and subsequently was found in the sands on the beaches in Mumbai, India and at Sasvane, Alibag and Uran (all towns in the coastal District of Raigad near Mumbai), creating a disaster for fishermen and fish habitats. Within four days, oil also reached the shores of the Gharapuri Island, near Mumbai, which hosts the archeologically important Elephanta Caves. Several acres of mangrove forests including newly germinated and growing saplings of mangroves were covered with free floating oil and weathered products of spilled oil.
Remediation or decontamination of sites contaminated with pollutants has been an active area of research in the field of environmental science and engineering, especially during the past three decades. Because of the ever increasing threat of pollution, the research in this area is becoming more intensified and there is an urgent need to develop technological solutions to a variety of contamination situations resulting from causative factors as stated earlier. There are two ways in which site remediation is addressed, namely in-situ on site and ex-situ on site solutions based on physico-chemical treatments. Another way of dealing with the problem is biological treatment.
In the case of in-situ on site clean-up operations undertaken by the Exxon Corporation in 1989 in Prince Williams Sound, Ak., USA, hot water jets mixed with oil dispersing chemicals were sprayed under pressure at the site of contamination. However, the above procedure could merely transfer free oil coating on surfaces like those of boulders, aggregates, pebbles, jetties or piers. As a result, dislodged oil and weathered oily residues got deposited onto superficial layers of sandy beaches, mud flats and coastal sediments and eventually percolated into deeper layers of sediments creating additional secondary pollution. Therefore, efforts were also made to skim-off floating oil from the water surface. The procedure has been only partially successful in the clean up operations thereby leaving most of the oil pollution unattended in the marine environment. Clearly, there has not been any effective sand or sediment or silt cleaning technology or method available for decontamination of pollutant-loaded earth solids. Use of jets of hot water and chemical solutions to wash and clean surfaces as stated earlier, only aggravated the problem of contamination of sands, sediments and silts on the coasts.
In the events of oil spills, bacteria present in the coastal silt, sediments and sands do get eventually acclimated to the polluted environment and develop ability to denature the pollutants in due course of time as is evident from studies conducted on several species of bacteria and their strains isolated from the polluted coastal sites. Because of this adaptation of the bacteria, in fact, the native flora and fauna got affected on the polluted marine coast and the entire ecosystem got altered.
Bioremediation of contaminated sites was carried out using specific cell cultures containing active beneficial species isolated and selected from the polluted sites and cultivated in the laboratory. Bioremedy was also tried by spraying genetically modified microorganisms and enzyme-mediated formulations prepared in the laboratory or cultured and formulated using biotechnological methods. The degradation rates for targeted pollutants in open natural systems with the help of microbes cultivated in laboratory environment is known to be slow and compromised due to the interference of other microbial flora at the contaminated site. The microbes also may not reach the intricate places where the pollutants have gotten diffused to and microbial population may not get sustained in the open environment. As a result, a critical concentration of the desirable microorganism or desirable mixed culture of a consortium of microorganisms remains so low that it does not produce desirable results and it fails to create ecological niche for itself.
The micro-organisms selected from naturally occurring contaminated sites and cultivated for real-life bio-remediation operations or designer microbes (genetically modified to denature a given pollutant) if applied in real-life situations in the so-called open systems may face difficulty in performing in the presence of high concentrations of oils and weathered oil-products at a given contaminated site. The high concentrations of pollutants may prove to be toxic to them and may prove to be detrimental to their community.
The various in-situ on-site treatments as stated above employ dedicated treatment plants installed in-situ onsite and have shown limited success in real situations and have several limitations. Because of the non-homogeneity of soil, sediment or sand, the ability to engineer the contaminated site and to achieve uniform cleaning of contaminated areas is reduced. As a result the in-situ techniques are not very efficient and effective. Cost and erection time for the plants is very huge. Invariably multiple installations of in-situ onsite treatment plants are required as contaminated beaches extend to tens or hundreds of kilometers. Because of this, the cost of in-situ techniques ends up typically becoming prohibitive and, therefore, in realistic situations they may not be economically viable.
Earlier research has described the effectiveness of desorption for removing contaminants from sand or soil [Rao, B H, Swaminathan, R., and Asolekar, S. R. (2001). Washing of Marine Coastal Sand in a Batch Reactor: Sorption and Desorption of BTEX. J Air & Waste Manage Assoc., vol. 51, pp. 1043-1059; and Rao, B H and Asolekar, S. R. (2001). QSAR Models to Predict Effect of Ionic Strength on Sorption of Chlorinated Benzenes and Phenols at Sediment-Water Interface. Water Research, vol. 35, pp. 3391-3401].
In reality, however, such techniques envisage transportation of polluted materials from the contaminated sites to the reactors erected at a location for decontamination and transportation of cleaned sand or soil back to the contamination sites. Such techniques require dedicated treatment plants at the location and huge sand and sediment washing reactors and solids—wastewater separation devices permanently erected and installed at the location. As a result, the cost is increased substantially. The reactors require massive foundations. Provision of effective foundation for the reactors would be a difficult task in sandy beaches or industrially or commercially contaminated sites.
Transportation of huge quantities of excavated soil from the site of excavation to the reactors and back to the excavation site is very expensive and cumbersome. Further, installation of the treatment plant at one location alone would not be sufficient to provide remediation service to a large area as contaminated beaches extend to a long distance.
Alternative is to have multiple treatment plants which will increase the cost correspondingly. A stationary facility for remediation is also not very effective and useful since accidents of spillage of oil may happen anywhere. Also, development of dedicated reactors and washing plants involves capital investment which can be amortized only if the reactors and plants are utilized to the optimum. Erection time for such plants is also very long.
It is evident from the above state of the technology of environmental remediation that there are no effective methods and equipments available for addressing and managing disasters like marine oil spills causing contamination of sandy beaches and coastal ecosystems or land-based disasters created by large scale spills of toxic and hazardous chemicals or disasters caused by the negligent disposal of toxic and hazardous wastes into water bodies and dump-sites. There is thus need for effective, economical and easy to implement method and system to remedy or decontaminate polluted environment from hazardous substances.